1. Field of Invention
This invention pertains to a method and system in which content is sent or can be utilized only by sinks that are within a specified maximum distance from a source.
2. Description of the Prior Art
The fundamental problem addressed by the invention is that there is currently no way to guarantee (with high confidence) that a content sink device (e.g., television) is actually within the same users home, business, or other geographically-limited region as the content source device (e.g., a set-top box) to which the content owner desires to limit the distribution, reproduction, or playback of his content. For example, generally, if the source and the sink are connected through the Internet then they might be on opposite sides of the earth.
A case of special concern involves the use of Digital Transmission Content Protection (DTCP) (http://www.dtcp.com) protocol for copy protection over IEEE 1394, USB, MOST, and IP networks. DTCP only “secures” the link between the (5C) source and sink; there is no built-in notion of proximity between the source and sink devices. Part of the problem is solved by the (5C) standard, which guarantees (with high confidence) that a receiver is actually authorized to decode/store/playback (5C) encoded content. However, it is possible that the authorized (5C) receiver may be located too far away from the (5C) source, according to the content owner. So the (5C) standard per se does not solve the problem of limiting the geographic diffusion of content. Techniques that attempt to identify the receiving content user, for example by having the user enter a PIN or insert a smart card into the receiver are helpful in limiting the undesired diffusion of content, but do not address the fundamental problem that the receiving user may have placed the receiving device “too far away” from the potential content source. There are many known ways of determining the geographic location of an object.
“Triangulation” has been used for many years to establish the location of objects that emit electromagnetic radiation. This involves the use of two or more receivers with directional antennae and a geographic information database, such as a map. Given the known locations and directions of maximal received signal strength at the receivers, it is easy to find the transmitter location as the point at which lines drawn on the map from each receiver to “infinity” in the direction of maximal signal strength, intersect. In this case, the cooperation of the transmitter is not necessary, and, in fact, triangulation is often employed to locate unauthorized transmitters. A triangulation-based approach may serve the purpose of this invention, but only if the content receiver emits electromagnetic radiation, and two or more triangulation receivers are available.
More recently, it has become common for receivers to establish their positions using a Global Positioning System (GPS), which relies on measuring the differential delays of several signals transmitted from an array of GPS satellites. If the content receiver includes a GPS receiver and “return-channel” transmitter, it can convey its location back to the content source. The content source may be assumed to include a GPS receiver and/or a geographic database and means for calculating its distance from the content receiver. However, GPS does not work reliably indoors, and a receiver may be set with an incorrect location code as well.
Localization techniques that use so-called “ultra-wideband (UWB) radio” have also recently been described. For example, see U.S. Pat. No. 6,002,708: “SPREAD SPECTRUM LOCALIZERS”, assigned to Aether Wire & Location, Inc.
Techniques are also known whereby proximity of receivers to transmitters is established using Round-Trip Time (RTT) measurements between a transmitted signal from the source to the sink and the corresponding return signal. In the case of a single cooperating transmitter-receiver pair, this RTT measurement may be sufficient to establish that the receiving device is “close enough” to the transmitting device that the receiving device should be authorized to decode/store/playback a specified amount of content.
One proposed, anti-diffusion solution involves the source setting the “Time to Live” (TTL) field to three in (IP) packets. This assumes that packets will traverse no more than three routers within a home network, else it is assumed that they have left the bounds of the home (some research shows that packets must typically traverse six routers to get beyond the ISP to which the home network is connected) and the third router encountered by the packet should “kill” (i.e., discard) it. A second potential solution is the measurement of RTT using DTCP-level ping messages.
Another proposed solution is to require that the Wired Equivalency Protocol (WEP) be employed on (partly or wholly) wireless local networks. This addresses the cases of “unintentional sharing” of content that may occur simply by virtue of an unintended receiver being within range of a wireless content source due to:                1. innocent co-location, e.g., reception by one's neighbor, or        2. eavesdropping, e.g., by “freeloaders” parking vehicles within reception range of unprotected wireless networks.        
The article http://www.spectrum.ieee.om/WEBONLY/publicfeature/iul03/e911.html describes a number of localization techniques, including other “old” techniques like LORAN not referenced above. It specifically mentions Aether Wire & Location Inc. (Nicasio, Calif.), whose patent is referenced above.
International Patent Application number WO 03/075125 A2 assigned to Enterasys Networks, mentions the use of RTT, among other mechanisms, as a means to authenticate receiving devices in a “location aware data network”.
International Patent Application WO 01/93434 A2, assigned to XtremeSpectrum, describes the use of RTT and triangulation to enable/disable a function in a remote device in a network comprising devices that communicate over a UWB wireless medium.
U.S. patent application 20020136407 by Denning, et. al., describes a system/method in which data may only be decrypted at (a) specified geographic location(s). Location information is typically supplied by the GPS.